IC chips or LSI chips are typically bonded onto a circuit board by soldering. The soldering steps comprise: application of a cream type solder (hereinafter referred to as “soldering cream”) onto electrodes mounted in the board using a screen printing machine; coating the lead wires of the chips with soldering cream and heating the cream type solder using a reflowing machine e.g. an oven. Insufficient application of soldering cream may cause the soldering to fail. It is therefore important that the coating state of the cream solder be inspected before the chips are mounted onto the board. In the case of BGAs (Ball Grid Arrays), an input pad and an output pad are arranged on the back of the package. Once the BGA chips are bonded onto the board, inspection of soldering conditions are too late. Soldering conditions must be inspected before the BGA chips are bonded onto the board.
To accurately detect defects, the inspection apparatus for inspecting the soldering cream coating conditions must provide a very high resolution of the captured image of the board with a resolution corresponding to the packaging density. Moreover, due to time constraints in the packaging process, the inspection operation must be conducted quickly and without causing a delay in shipment. It should be noted that one bad product found in a shipment generates additional jobs such as collection, repair, re-shipment that would not have been required otherwise. Profits from sales may not cover the cost of all these additional jobs.
Conventional inspection apparatus inspects the soldering cream coating condition on the body to be inspected by measuring the area within which a soldering cream is coated. Since it is essential for an appropriate amount of soldering cream to be coated onto a chip to effectuate normal soldering, the appropriate amount and not the coating area should be measured to perform an accurate inspection. Without a highly accurate volume measurement of the soldering cream, there is no accurate inspection. Accordingly, to perform a highly accurate inspection, the volume measurement of the soldering cream is essential.
An apparatus which irradiates a line pattern onto a board through a slit in a light projector with the image of the board captured using a camera to analyze the shape of the soldering paste is taught in Japanese unexamined patent (Kokai) No. H05-187838.